The Carotene and Retinol Efficacy Trial (CARET) is a Phase IV chemoprevention study which tests the efficacy of the combination of retinol and beta-carotene to prevent lung cancer in two high-risk populations (a) heavy smokers recruited from insurance-based sources, and (B) current and former workers with heavy occupational asbestos exposure recruited from workers' compensation and employment-based sources. The double-blind two-arm randomized protocol compares placebo to a daily combination of 30 mg beta-carotene plus 25,000 IU retinol. Current assumptions and projections indicate that the full scale Efficacy Trial will be capable of detecting significant reductions in lung cancer incidence in the two high-risk groups combined and larger reductions in either subgroup alone. An adequate number of study sites have been identified for accrual of 4000 asbestos-exposed subjects. One additional major site ins needed as planned in 1988, to achieve the desired recruitment of smokers (13,000 -14,000 total.) The participation of University of California, Irvine (UCI) in CARET will focus on the recruitment of heavy smokers from the subscribers lists of the Kaiser Permanente, Blue Cross and FHP, Health Plans for selected counties in Southern California (Orange, Riverside, San Bernardino). During the first three years of UCI's participation (1991-1994), we propose to recruit, enroll and follow 4300 subjects randomized according to the specifications of the CARET protocol. The UCI site -has the population base from which to recruit additional participants should accrual be below projections at the other study sites. We will provide all necessary data to evaluate recruitment, accrual, coordination and costs to generate the best estimates of the remaining needs for the full-scale enrollment and follow-up.